This invention relates to an image forming apparatus provided with a clamshell-type mechanism for opening a main body on one side.
There have been known image forming apparatus, such as facsimile machines, copying machines, and printers, having a main body including an upper body and a lower body. The upper and lower bodies are connected at a pivot shaft on one side to open the main body on the other side. Such structure is intended to reduce the size of apparatus, and provide convenience in removing jammed copy paper and easy access to internal elements for inspection and maintenance.
An apparatus provided with such an opening mechanism has a normal state when the upper body is engagedly mounted on the lower body. When consideration is given to structural strength and stability as well as to ease of maintenance and paper jam treatment, there arise certain limitations in the arrangement of individual mechanical members and internal modules. Due to these limitations, it is difficult to reduce the size, weight and cost of the apparatus.
With recent improvements in the quality of synthetic resins and advances in resin molding technology, it would be preferable to utilize molded resins for mechanical members. However, since the upper body of such apparatus is required to have a specified structural strength to support relatively heavy internal modules which may include image reading means and image forming means, for example, it is a common practice to mainly employ iron plates and other metal members.
In particular, if the apparatus is configured to accommodate removable image reading and forming means in the upper body for easy assembly and maintenance, the upper body will be subjected to complex stresses when the apparatus is opened and closed, or when the internal modules are removed and mounted. Since such stresses tend to cause structural deformation and misalignment, metal members are extensively used to achieve the desired positioning accuracy of the internal modules although this will result in an increase in the weight of the upper body. Furthermore, as the upper body becomes heavier, the lower body is required to have more weight in order to bring down the center of gravity of the whole apparatus for its overall balance and stability. This is why it has been difficult to reduce the weight of the apparatus.
Since the apparatus provided with such an opening mechanism has its normal state when the upper body is entirely mounted on the lower body, it is extremely important to properly control the descending position of the upper body in relation to the lower body. To meet this requirement, the conventional apparatus is provided with separate vertical and horizontal positioning members. The vertical positioning member sets a limit to the descending stroke of the upper body's swinging side to determine its closed position in the vertical direction while the horizontal positioning member restricts lateral displacement of the upper body in the closed position to prevent its horizontal displacement in relation to the lower body. The vertical and horizontal positioning members work together to set the relative position of the upper and lower bodies when they are closed.
It is to be noted that the provision of the separate vertical and horizontal positioning members results in an increase in the number of mechanical members, making the mechanical structure complex. If there occurs a mutual displacement between the upper and lower bodies, remedy is rather complicated because the vertical and horizontal positioning members must be adjusted individually.
To easily remove jammed copy paper, it is preferable to divide the apparatus into upper and lower bodies along a paper path. With this configuration, it would be possible to expose the paper path by opening the apparatus to remove jammed copy paper. One approach to achieve such structure in a compact design is to provide the apparatus with a paper feeding mechanism in an upper portion of the lower body, a copy paper cassette for storing a stack of copy paper sheets inside the lower body, and a paper inverting mechanism for quickly turning the feed direction of the copy paper sheet fed from the Copy paper cassette to the paper feeding mechanism upward.
As an example, the apparatus may be provided with a feed roller assembly for sequentially feeding sheets of copy paper from the copy paper cassette. The feed roller assembly comprises a rotating shaft carrying one or more pieces of friction rollers at intermediate portions. One end of the rotating shaft is connected to a drive mechanism. The rotating shaft is usually fitted into bearing holes in side members and retained by E-rings at both ends, for example, for restricting its longitudinal displacement, yet allowing the shaft to rotate.
On the other hand, the paper feeding mechanism usually comprises a pair of registration guide rollers, for example, one being a driving roller and the other being a driven roller, for conveying the copy paper fed from the copy paper cassette to a photosensitive drum. The registration rollers are mounted on side members at their respective positions. Consequently, an appropriate pressure is produced between the two registration rollers without causing longitudinal displacement as they rotate.
Although the above-mentioned feed roller assembly and registration guide rollers are arranged to provide an accurate feed of the copy paper sheet without displacement of individual rollers, their structural complexity impairs productivity and serviceability, requiring complicated procedures for assembly and replacement of individual components.
It is an object of the present invention to provide an image forming apparatus which has overcome the above-mentioned problems.
It is another object of the present invention to provide an image forming apparatus which is compact and light as well as having a sufficient strength, and simple in construction, and assure easy maintenance.